Use strings.Cut() instead of string.SplitN()

[ash2k]

strings.Cut() generates less garbage as it does not allocate the slice to hold parts. See also open-telemetry/opentelemetry-go#4049.

[codecov]

Codecov Report

Merging #3822 (3ece61b) into main (95167fd) will not change coverage.
The diff coverage is 100.0%.

❗ Current head 3ece61b differs from pull request most recent head f7259c6. Consider uploading reports for the commit f7259c6 to get more accurate results

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3822   +/-   ##
=====================================
  Coverage   70.1%   70.1%           
=====================================
  Files        149     149           
  Lines       7133    7133           
=====================================
  Hits        5004    5004           
  Misses      1998    1998           
  Partials     131     131           

Impacted Files	Coverage Δ
.../google.golang.org/grpc/otelgrpc/internal/parse.go	100.0% <100.0%> (ø)